Stereospecific polymerization of 2‐vinylpyridine

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Abstract
Some metalloorganic or metal amide compounds of very electropositive metals, such as lithium, sodium, beryllium, magnesium, and aluminum, cause the polymerization of 2‐vinylpyridine. Whereas the compounds of beryllium and of aluminum furnish slightly crystalline 2‐vinylpyridine polymers, by using magnesium derivatives it is possible to obtain polymers which are highly crystalline by x‐rays. The results obtained from the systematic study of the polymerization in the presence of amides or of metalloorganic compounds of magnesium are reported. In particular, it has been examined the influence of the monomer/catalyst molar ratio, of the temperature, of the polymerization time, and of the nature of the substituents bound to magnesium, on the course of the polymerization and on the properties of the obtained polymers. Examination by IR spectrography allowed us to conclude that at least a part of the macromolecules contain, as endgroup, the organic groups which were initially bound to the metal in the compounds used as catalyst. The stereospecificity of the process must be ascribed to the possibility of coordination of the catalyst to the monomer molecules entering the growing chain. In fact, the addition of organic Lewis bases to the system, causes the reduction or the disappearence of stereospecificity. The obtained results allowed us to conclude that the stereospecific polymerization of 2‐vinylpyridine takes place by an anionic coordinated mechanism. 4‐Vinylpyridine, in the presence of catalysts which are stereospecific for the polymerization of 2‐vinylpyridine, gives amorphous noncrystallizable polymers. That was ascribed by us to the fact that the nitrogen atom, in the case of 4‐vinylpyridine is too far from the vinyl double bond to form, with the catalyst, an addition complex able to give the same orientation to all the monomer molecules, at the very moment of the polymerization.

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